1. Field of the Invention
The present invention relates to fuel systems for internal combustion engines.
2. Prior Art
The terms freezing and melting are used herein in a general sense, and not necessarily in a strict technical sense. By way of example, oils tend to not have a clear freezing temperature, but rather steadily increase in viscosity with decreasing temperature, loosing their ability to flow or be poured to an increasing extent with decreasing temperatures. They also generally do not undergo a change of phase, so do not have a latent heat of fusion associated therewith that must be overcome to melt. Still, they do freeze in the sense of becoming substantially motionless when subjected to conditions where a liquid would flow or pour.
Internal combustion engines have been designed and constructed to run on various fuels. A typical passenger car engine runs on gasoline, which has a freezing point much lower than normally encountered, even in cold climates. Consequently, other engine starting problems such as oil viscosity, battery cranking power, etc, are encountered well before gasoline freezes, or at least becoming too viscous to flow to the carburetor or fuel injectors. Diesel fuel however, is another story, as it can become a problem for somewhat rarely encountered cold weather. Alternate fuels such as biodiesel fuels are particularly troublesome, as such fuel will exhibit very high viscosity, or at least not freely flow at winter temperatures often encountered in the more northern parts of the 48 states. Consequently if these fuels are to find common or somewhat common use, a solution must be found to this problem.
The typical cold weather problem encountered with diesel and biodiesel fuels is not the inability to pump the fuels, or to inject the same into the combustion chamber, as one can design a fuel pump to provide the required pumping force (pressure), and can use electrical heaters on the fuel line for starting and exhaust heat fuel heaters for continually heating the fuel as required, once the engine is started. However, the problem is in getting the cold fuel into the pump inlet. Typically in such engines, the fuel pump may pump that which is in the pump, but shortly after the engine starts, the fuel flow stops because of no fuel is running into the pump inlet, and the pump runs dry.